Polyolefin compositions used for making embossed sheets with improved gain retention

ABSTRACT

Embossed sheets having improved grain retention can be made from a polyolefin composition containing a propylene polymer material and a partially crosslinked thermoplastic olefin elastomer composition that includes (1) 20-80 parts by weight of a thermoplastic elastomer containing (a) from 20 to 70% of a propylene homopolymer having an isotactic index greater than 90, or a crystalline propylene copolymer with ethylene and/or a 4-8 C alpha-olefin having a polymerized propylene content greater than 85% and an isotactic index of greater than 85%; (b) from 30 to 75% of an amorphous ethylene-propylene or ethylene-butane-1 copolymer, which is xylene soluble at room temperature and contains from 30 to 70% polymerized ethylene, and (c) from 3 to 30% of a semi-crystalline ethylene-propylene or ethylene-butene-1 copolymer that is xylene insoluble at room temperature and contains greater than 90% polymerized ethylene, and (2) 80-20 parts by weight of an ethylene/propylene/diene terpolymer rubber containing 1 to 10% of a polymerized diene and 30 to 70% polymerized ethylene. Large parts such as automobile door and instrument panels can be formed from these sheets.

This application is a continuation of Ser. No. 08/757,014 filed Nov. 26,1996, now abandoned.

FIELD OF THE INVENTION

This invention relates to a polyolefin composition comprising (A) apropylene polymer material and (B) a partially crosslinked thermoplasticolefin elastomer composition.

BACKGROUND OF THE INVENTION

With advances in polyolefin technology, the use of polypropylenematerials, particularly thermoplastic olefin materials (TPOs), inautomotive applications has increased dramatically, replacing nonolefinmaterials such as acrylonitrile/butadiene/styrene terpolymer, polyvinylchloride, and polycarbonate. Thermoplastic olefins are uncrosslinkedblends of olefin polymers and polyolefin elastomers. New reactor productTPOs are finding use in areas such as interior trim (e.g., dashboardsand door panels) due to their soft feel, thermoformability, andresistance to ultraviolet light and heat.

The process of producing these parts involves the following steps: (a)extrusion or calendering of the TPO sheet, (b) embossing (on- oroff-line) of the extruded or calendered sheet to produce a textured or"grained" surface, (c) laminating and/or bonding extruded or calenderedsheet to a foam or fabric for softness, (d) topcoating or painting thesheet for UV, scratch and mar resistance, and (e) forming the final partor other article from the sheet by thermoforming or low pressureinjection molding.

U.S. Pat. No. 5,338,801 describes a polyolefin composition comprising(A) 70 to 90% of a propylene polymer material and (B) 30 to 10% of anolefin polymer material selected from the group consisting of (1) apartially crosslinked thermoplastic olefin elastomer compositionconsisting of a thermoplastic elastomer and an olefin rubbercomposition, (2) an uncrosslinked ethylene-propylene-conjugated dieneterpolymer rubber, and (3) mixtures of (B)(1) and (B)(2). Thecomposition provides low gloss after processing with retention ofphysical and mechanical properties.

A major drawback of TPOs has been their inability to retain embossedgrain after the sheet is thermoformed into a large part such as adashboard. The low melt strength and shear thinning that are typical ofTPOs result in loss of the textured surface and walls that are too thinwhen the TPOs are formed into parts or other articles.

SUMMARY OF THE INVENTION

The polyolefin composition of this invention comprises, by weight,

(A) from 40 to 70% of a propylene polymer material consistingessentially of:

(1) from 10 to 50% of a propylene homopolymer having an isotactic indexof about 80 to about 99%, or a copolymer selected from the groupconsisting of (a) propylene and ethylene, (b) propylene, ethylene and aCH₂ ═CHR alpha-olefin, where R is a C₂₋₈ straight or branched alkylgroup, and (c) propylene and an alpha-olefin as defined above in (1)(b),the copolymer containing from 85 to 99% propylene and having anisotactic index greater than 80 to about 98%,

(2) from 3 to 20% of a semi-crystalline, essentially linear copolymerfraction having a crystallinity of about 20 to about 60% by differentialscanning calorimetry (DSC), wherein the copolymer is selected from thegroup consisting of (a) ethylene and propylene containing over 50%ethylene; (b) ethylene, propylene, and an alpha-olefin as defined abovein (1)(b), containing from 1 to 10% of the alpha-olefin and over 50% upto 98% of both ethylene and alpha-olefin; and (c) ethylene and analpha-olefin as defined in (1)(b) containing over 50% up to 98% of thealpha-olefin, which copolymer is insoluble in xylene at room or ambienttemperature, and

(3) from 40 to 80% of a copolymer fraction selected from the groupconsisting of a copolymer of (a) ethylene and propylene, wherein thecopolymer contains from 20% to less than 40% ethylene; (b) ethylene,propylene, and an alpha-olefin as defined in (1)(b), wherein thealpha-olefin is present in an amount of from 1 to 10%, and the amount ofethylene and alpha-olefin present is from 20% to less than 40%; and (c)ethylene and an alpha-olefin as defined in (1)(b), containing from 20 toless than 40% of the alpha-olefin, and optionally containing 0.5 to 10%of a diene, the copolymer fraction (3) being soluble in xylene atambient temperature, and having an intrinsic viscosity of from 1.7 to3.0 dl/g, wherein the total amount of fractions (2) and (3), based onthe total olefin polymer composition is from about 65% to 80%, theweight ratio of fractions (2)/(3) is from 0.1 to about 0.3, and thetotal content of ethylene or C₄₋₈ alpha-olefin or combination thereof infractions (2)+(3) is less than 50%, and

(B) from 60 to 30% of a partially crosslinked thermoplastic olefinelastomer composition consisting essentially of:

(1) 20-80 parts by weight of a thermoplastic elastomer consistingessentially of:

(a) from 20 to 70% of a propylene homopolymer having an isotactic indexgreater than 90, or a crystalline propylene copolymer with ethyleneand/or a C₄₋₈ alpha-olefin having a propylene content greater than 85%and an isotactic index of greater than 85%;

(b) from 30 to 75% of an amorphous ethylene-propylene or ethylene-butenecopolymer fraction, optionally containing from 1 to 10% of a diene,which is xylene soluble at room temperature and contains from 30 to 70%ethylene, and

(c) from 3 to 30% of a semi-crystalline ethylene-propylene orethylene-butene copolymer that is xylene insoluble at room temperatureand contains greater than 90% ethylene, and

(2) 80-20 parts by weight of an ethylene/propylene/diene terpolymerrubber containing 1 to 10% of a diene and 30 to 70% ethylene.

The addition of the partially crosslinked TPO elastomer composition tothe propylene polymer material produces sheet materials exhibitingsignificant improvement in grain retention and reduction in shearthinning. Large parts such as automobile door and instrument panels canbe formed from these sheets.

DETAILED DESCRIPTION OF THE INVENTION

All parts and percentages used in this specification are by weightunless otherwise specified. Ambient or room temperature is approximately25° C.

Component (A) used in the composition of the present invention is apropylene polymer material consisting essentially of:

(1) from 10 to 50% of a propylene homopolymer, preferably from 10 to40%, and most preferably from 20 to 35%, having an isotactic index ofabout 80 to about 99%, and preferably from 85 to 99%, or a copolymerselected from the group consisting of (a) propylene and ethylene, (b)propylene, ethylene and a CH₂ ═CHR alpha-olefin, where R is a C₂₋₈straight or branched alkyl group, and (c) propylene and an alpha-olefinas defined above in (1)(b), wherein the copolymer contains from 85 to99%, and preferably from 90 to 99% propylene and has an isotactic indexgreater than 80 to 98%, preferably greater than 85 to about 98%,

(2) from 3 to 20% of a semi-crystalline, essentially linear copolymerfraction, preferably from 7 to 15%, having a crystallinity of about 20to about 60%, by differential scanning calorimetry (DSC), wherein thecopolymer is selected from the group consisting of (a) ethylene andpropylene containing over 50% ethylene; (b) ethylene, propylene, and analpha-olefin as defined above in (1)(b), containing from 1 to 10% of thealpha-olefin and over 50% up to 98%, preferably from 80 to 95%, of bothethylene and alpha-olefin; and (c) ethylene and an alpha-olefin asdefined in (1)(b), containing over 50% up to 98%, preferably from 80 to95%, of the alpha-olefin, which copolymer is insoluble in xylene at roomor ambient temperature, and

(3) from 40 to 80% of a copolymer fraction, preferably 50 to 70%,selected from the group consisting of a copolymer of (a) ethylene andpropylene wherein the copolymer contains from 20% to less than 40%,preferably from 20 to 38%, most preferably 25 to 38% ethylene, (b)ethylene, propylene, and an alpha-olefin as defined in (1)(b), whereinthe alpha-olefin is present in an amount of from 1 to 10%, preferablyfrom 1 to 5%, and the amount of ethylene and alpha-olefin present isfrom 20% to less than 40%, and (c) ethylene and an alpha-olefin asdefined in (1)(b), containing from 20 to less than 40%, preferably 20 to38%, and most preferably 25 to 38% of the alpha-olefin, and optionallycontaining 0.5 to 10%, preferably 1 to 5%, of a diene, the copolymerfraction (3) being soluble in xylene at ambient temperature, and havingan intrinsic viscosity measured in tetrahydronaphthalene at 135° C.preferably of from 1.7 to 3.0 dl/g, wherein the total amount of ethyleneunits or the alpha-olefin units in the olefin polymer composition or ofethylene and the alpha-olefin units when both are present in the olefinpolymer composition is from 15 to 35%, the total amount of fractions (2)and (3), based on the total olefin polymer composition is preferablyfrom about 65% to 80%, the weight ratio of fractions (2)/(3) ispreferably from 0.1 to about 0.3 and the total content of ethylene orC₄₋₈ alpha-olefin or combination thereof in fractions (2)+(3) is lessthan 50%, and preferably from 20 to 45%.

The propylene polymer material of component (A) has at least one meltpeak, determined by DSC, present at temperatures higher than 120° C.,and at least one peak, relative to the vitreous transition, present attemperatures from -10° C. and -35° C. In addition, these materials havea flexural modulus of less than 150 MPa, generally from 20 and 100 MPa;a tensile strength at yield of from 10 to 20 MPa; elongation at breakover 400%; a tension set, at 75% strain, from 20% to 50%; a Shore Dhardness from 20 to 35; a haze value of less than 40%, preferably lessthan 35%, and do not break (no bridle impact failure) when an Izodimpact test is conducted at -50° C. Component (A) is present in anamount of from 60 to 40%, preferably 50 to 40%, of the totalcomposition.

Component (A) can be prepared by a polymerization process comprising atleast two stages, where in the first stage the propylene, or propyleneand ethylene or the alpha-olefin, or propylene, ethylene andalpha-olefin are polymerized to form component (A)(1), and in thefollowing stages the mixtures of ethylene and propylene or alpha-olefin,or propylene, ethylene and alpha-olefin, and optionally a diene, arepolymerized to form components (2) and (3).

The polymerization can be conducted in the liquid phase, gas phase, orliquid-gas phase using separate reactors, all of which can be doneeither by batch or continuously. For example, it is possible to carryout the polymerization of component (A)(1) using liquid propylene as adiluent, and the polymerization of components (2) and (3) in the gasphase, without intermediate stages except for the partial degassing ofthe propylene. The preparation of the propylene polymer material isdescribed in more detail in U.S. Pat. No. 5,212,246, the process ofwhich is incorporated herein by reference.

Component (B) of the present invention is a partially crosslinkedthermoplastic olefin elastomer composition consisting essentially of:

(1) 20-80 parts by weight of a thermoplastic elastomer compositionconsisting essentially of:

(a) from 20 to 70%, preferably from 20 to 50%, of a propylenehomopolymer having an isotactic index greater than 90, preferablygreater than 98%, or a crystalline propylene copolymer with ethyleneand/or a C₄₋₈ alpha-olefin having a propylene content greater than 85%and an isotactic index of greater than 85%,

(b) from 30 to 75%, preferably from 30 to 50%, of an amorphousethylene-propylene or ethylene-butene copolymer fraction, optionallycontaining from 1 to 10%, preferably 1-5%, of a diene, that is xylenesoluble at room temperature and contains from 20 to 70% ethylene, and

(c) from 3% to 30%, preferably from 5 to 20%, of a semi-crystallineethylene-propylene or ethylene-butene copolymer that is xylene insolubleat room temperature and contains greater than 75% ethylene, preferablygreater than 85%, and

(2) 80-20 parts by weight of an ethylene/propylene/diene terpolymerrubber containing 1 to 10% diene and 30 to 70% ethylene.

In the compositions of the present invention component (B) is present inan amount of from 60 to 30%, preferably from 55 to 30%, and mostpreferably 50 to 30%.

The C₄ -C₁₀ alpha-olefins useful in the preparation of components (A)and (B) of the polyolefin composition of this invention includebutene-1; pentene-1; hexene-1; 4-methylpentene-1, and octene-1.

The diene, when present, is typically a butadiene; 1,4-hexadiene;1,5-hexadiene, or ethylidenenorbornene.

Component (B) is prepared by adding a peroxide curing system comprisingan organic peroxide and at least one crosslinking aid selected frompoly(1,2-butadiene) and furan derivatives, to a mixture of components(B)(1)(a), (b), and (c) and (B)(2), and subjecting the mixture to curingconditions while masticating the mixture to bring about the desireddynamic partial cure.

Preferably components (B)(1)(a), (b) and (c) are formed in a reactor orseries of reactors in at least two stages by first polymerizingpropylene to form component (a) and then polymerizing ethylene andpropylene or ethylene and butene in the presence of component (a) andthe catalyst used in the first stage to form components (b) and (c). Thepolymerization can be conducted in the liquid or gas phase or inliquid-gas phase. In the alternative, components (a), (b), and (c) caneach be prepared separately and then mixed by melt-kneading or meltblending.

The term "partially cured" means that the degree of curing, in terms ofthe gel content, is at least 80% and no more than 94% in cyclohexane.Preferably, the gel content is from 85 to 92%. Percent gel content isdetermined by soaking a weighed 1.5"×0.75"×0.080" test specimen in about100 ml cyclohexane at about 23° C. for 48 hours, removing the sample anddrying to constant weight (about 72 hours) in a vacuum oven at 80° C.The % gel is calculated as: ##EQU1##

The preparation of the partially cured thermoplastic elastomer isdescribed in more detail in U.S. Pat. No. 5,196,462, the process ofwhich is incorporated herein by reference.

The compounding or melt blending of components (A) and (B) of thepresent invention can be carried out on an open roll, in an internalmixer (Banbury or Haake mixers), and single-screw or twin-screwextruders.

The polyolefin composition of the present invention can also containother conventional additives, for example, antioxidants, stabilizers,extender oils such as paraffinic and naphthenic oils, fillers such asCaCO₃, talc and zinc oxide, or flame retardants.

Evaluating grain retention is highly subjective, since there are nostandardized tests to measure this property per se. The aestheticappearance of the final part is presently the industry standard indetermining specimen acceptability.

In order to evaluate the relative grain retention of olefin polymermaterials, the appearance of thermoformed sample specimens prepared fromembossed sheets when viewed with the naked eye was compared with thecompression set value of the present industry standards, i.e, polyvinylchloride (PVC) and blends of PVC and acrylonitrile/butadiene/styrene(ABS). Both PVC and PVC/ABS blends had good grain retention. Compressionset measures the percentage to which a polymer remains compressed aftercompression under standard conditions, i.e., 22 hours @212° F. accordingto ASTM-395, Method B. For example, 100% compression set translates to asample that when compressed remains 100% compressed and does not recoverto its original dimensions. Conversely, a sample with 0% compression setrebounds to 100% of its initial dimensions. The lower the compressionset value, the better a material retains its original shape. PVC had acompression set value of 80 and the PVC/ABS blend a value of 78. From ameasurement of the compression set value of various materials it wasconcluded that a compression set value equal to or less than 85% wouldresult in a material with acceptable grain retention in automotiveparts.

EXAMPLE 1

This experiment demonstrates the effect on compression set value andgrain retention when various amounts of a propylene polymer material anda partially crosslinked thermoplastic elastomer composition were blendedtogether.

Each sample was compounded and pelletized on a 21/2" (30:1 L/D) singlescrew extruder using a barrel temperature of 450-500° F. with resultingmelt temperatures of 450 to 500° F. The screw was equipped with a mixingsection to ensure adequate melt blending. The polymer pellets from thecompounding step were subsequently formed into 0.040" flat sheets usinga 11/2" (30:1 L/D) single screw extruder equipped with a 91/2" sheetdie. Barrel temperatures ranged from 450 to 525° F. with resulting melttemperatures of 500-535° F.

Each sheet was embossed with an 18×16 square mesh screen using a heatedCarver press. Upper and lower press platens were heated to 250° F. Thescreen pattern was embedded into the sheet using a force of 10 tons for10 seconds.

The embossed sheet was formed into 3" diameter by 2" deep cylindricalcups using plug assist thermoforming. Both the plug and the mold wereheated to 100° F. Thermoforming processing conditions were optimized foreach sheet formulation so that a best-case comparison between eachformulation could be made. Grain retention was determined by examiningthe embossed parts with the naked eye after thermoforming. Thermoformedparts for each formulation were compared side-by-side and ranked frombest to worst, using retention of the embossed pattern and absence ofwall thinning as the main criteria.

Component (A) was a composition comprising:

(1) 100 parts by weight of a propylene polymer material comprising (a)33% propylene-ethylene random copolymer having an ethylene content of3.3% and an isotactic index, defined as the xylene insoluble fraction,of 94, (b) 8.3% semi-crystalline ethylene-propylene copolymer fractioncontaining ˜83% ethylene, and (c) 58.7% amorphous ethylene-propylenecopolymer fraction containing ˜22% ethylene,

(2) 0.2 parts by weight of Tinuvin 123 stabilizer, commerciallyavailable from Ciba-Geigy, per hundred parts of the propylene polymermaterial (pph).

(3) 0.2 pph (2-(2-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole),

(4) 0.2 pph Chimassorb 119 light stabilizer, commercially available fromCiba-Geigy, and

(5) 0.2 pph Irganox B-225 antioxidant (2,2-bis 3-3,5-bis(1,1-dimethylethyl)-4-hydroxy-benzene propanoate andtris(2,4-di-tert-butylphenyl) phosphite as a 50/50 blend) commerciallyavailable from Ciba-Geigy.

Component (B) was a composition comprising:

(1) 42.6% of a thermoplastic elastomer consisting of (i) 35% of apropylene homopolymer having an isotactic index, defined as the xyleneinsoluble fraction, of 97.5, (ii) 6.9% of a semi-crystallineethylene-propylene copolymer that is xylene insoluble at roomtemperature, (iii) 58.1% of an amorphous ethylene-propylene copolymerrubber that is xylene soluble at room temperature,

(2) 18.65% of an ethylene/propylene/ethylidenenorbornene terpolymerrubber containing 69% ethylene and 4% ethylidenenorbornene, having aMooney viscosity of 60 ML (1+4) at 125° C., commercially available fromEnichem.

(3) 6.4% CaCO₃,

(4) 1.86% ZnO,

(5) 0.32% tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)methane,

(6) 0.16% 4,4'-thio-bis-(6-tert-butyl-m-cresol),

(7) 21.31% paraffin oil,

(8) 1.49% 2,5-dimethyl-2,5-t-butyl-peroxyhexane, added as 50% activeperoxide on clay,

(9) 0.8% Struktol TR 016, a mixture of fatty acid salts and esters,commercially available from Struktol Company,

(10) 5.34% polybutadiene, added as 65% active polybutadiene on silica,and

(11) 1.07% zinc salt of mercaptobenzothiazole.

                  TABLE 1                                                         ______________________________________                                                                          Qualitative                                 Component                                                                             Component                 Grain                                       (A)(%)  (B)(%)     Compression Set Value                                                                        Retention                                   ______________________________________                                        90      10         90             Poor                                        80      20         87             Fair-good                                   70      30         85             Good                                        60      40         84             Good                                        50      50         75             Good                                        40      60         73             Good                                        30      70         65             Fair-Poor                                   ______________________________________                                    

The data show that when too much propylene polymer material (Component(A)) was present (>70%), grain retention was poor. When too muchpartially crosslinked thermoplastic olefin elastomer (Component (B)) waspresent (>60%), there was also inadequate grain retention.

Other features, advantages and embodiments of the invention disclosedherein will be readily apparent to those exercising ordinary skill afterreading the foregoing disclosures. In this regard, while specificembodiments of the invention have been described in considerable detail,variations and modifications of these embodiments can be effectedwithout departing from the spirit and scope of the invention asdescribed and claimed.

I claim:
 1. A polyolefin composition comprising, by weight,(A) from 40to 60% of a propylene polymer material consisting essentially of:(1)from 10 to 50% of a propylene homopolymer having an isotactic index,defined as the percent insoluble in xylene, of about 80 to about 99%, ora copolymer from monomers selected from the group consisting of (a)propylene and ethylene, (b) propylene, ethylene and a CH₂ ═CHRalpha-olefin, where R is a 2-8 C straight or branched alkyl group, and(c) propylene and an alpha-olefin as defined above in (1)(b), thecopolymer containing from 85 to 99% polymerized propylene and having anisotactic index, defined as the percent insoluble in xylene, greaterthan 80 to about 98%, (2) from 3 to 20% of an essentially linearcopolymer from monomers selected from the group consisting of (a)ethylene and propylene containing over 50% polymerized ethylene; (b)ethylene, propylene, and an alpha-olefin as defined above in (1)(b)containing from 1 to 10% of the polymerized alpha-olefin and over 50% upto 98% of both polymerized ethylene and polymerized alpha-olefin; and(c) ethylene and an alpha-olefin as defined in (1)(b), containing over50% up to 98% of the polymerized alpha-olefin, which copolymer isinsoluble in xylene at room or ambient temperature, and (3) from 40 to80% of a copolymer from monomers selected from the group consisting of(a) ethylene and propylene, wherein the copolymer contains from 20% toless than 40% polymerized ethylene; (b) ethylene, propylene, and analpha-olefin as defined in (1)(b), wherein the polymerized alpha-olefinis present in an amount of from 1 to 10%, and the amount of polymerizedethylene and polymerized alpha-olefin present is from 20% to less than40%; and (c) ethylene and an alpha-olefin as defined in (1)(b),containing from 20 to less than 40% of the polymerized alpha-olefin, andoptionally containing 0.5 to 10% of a polymerized diene, the copolymer(3) being soluble in xylene at ambient temperature, and having anintrinsic viscosity measured in tetrahydronaphthalene at 135° C. of from1.7 to 3.0 dl/g, wherein the total amount of (2) and (3), based on thetotal olefin polymer composition is from about 65% to 80%, the weightratio of (2)/(3) is from 0.1 to about 0.3, and the total content ofpolymerized ethylene or polymerized 4-8 C alpha-olefin or combinationthereof in (2)+(3) is less than 50%, and (B) from 60 to 40% of apartially crosslinked thermoplastic olefin elastomer composition havinga gel content of at least 80% and not greater than 94% in cyclohexaneand consisting essentially of:(1) 20-80 parts by weight of athermoplastic elastomer consisting essentially of.(a) from 20 to 70% ofpropylene homopolymer having an isotactic index, defined as the percentinsoluble in xylene, greater than 90, or a crystalline propylenecopolymer from propylene and comonomers selected from the groupconsisting of (i) ethylene, (ii) a 4-8 C alpha-olefin and (iii) ethyleneand a 4-8 C alpha-olefin, having a polymerized propylene content greaterthan 85% and an isotactic index, defined as the percent insoluble inxylene, of greater than 85%; (b) from 30 to 75% of an amorphousethylene-propylene or ethylene-butene-1 copolymer, which is xylenesoluble at room temperature and contains from 30 to 70% polymerizedethylene, and (c) from 3 to 30% of a semi-crystalline ethylene-propyleneor ethylene-butene-1 copolymer that is xylene insoluble at roomtemperature and contains greater than 90% polymerized ethylene, and (2)80-20 parts by weight of an ethylene/propylene/diene terpolymer rubbercontaining 1-10% polymerized diene and 30-70% polymerized ethylene. 2.The composition of claim 1, wherein the amount of component (B) is from50 to 30%.
 3. The composition of claim 1, wherein component (A)(1) is apropylene/ethylene copolymer, (A)(2) is an ethylene/propylene copolymer,and (A)(3) is an ethylene/propylene copolymer.
 4. The composition ofclaim 1, wherein component (B)(1)(a) is a propylene homopolymer,(B)(1)(b) is an ethylene/propylene copolymer, and (B)(1)(c) is anethylene(propylene copolymer.